Statistical tools
Quick Calcules from GraphPad site. Access here.
Free statistical calculations. Access here.
Effect size calculators. Access here.
About Pearson’s correlation test. Access here.
Interesting comments of Statistics interpretation. Access here.
Power and Size calculator. Access here.
Webpage dedicated to sample size calculation. Very useful! Contains instructions of how to apply. Calculator here. Instructions here (in Portuguese, from CEUA/CCS/USP)